The present invention relates to the filling of a pressurized gas container. In particular, the invention relates to the filling of the gas tank of vehicles operating with a fuel cell or those with an internal combustion engine operating with hydrogen.
Document EP 1 818 597 describes a filling method consisting in using two successive filling steps (the second filling step having a lower filling rate than the filling rate of the first step). This filling method is designed to improve the reliability of the measurements (for example the pressure and temperature measurements) and the precision of the amount of gas transferred during the filling. This method, although it does allow a relatively precise measurement of the transferred mass to be obtained, is, however, not very satisfactory for improving the filling speed.
The hydrogen tanks or containers on board a vehicle must be filled in at most a few minutes, preferably in less than five minutes, so that filling is compatible with the daily use of the vehicle by the user, i.e. so that the vehicle is out of service for the minimum amount of time.
Rapid pressurization of tanks causes the gas to heat up to high temperatures, which is liable to damage the walls of the tank. Thus, it is therefore very important not to exceed this temperature limit value given by the tank manufacturer.
The gas heats up because, on the one hand, of the Joule-Thomson effect, i.e. heating caused by the pressure difference between the hydrogen source and the tank, and, on the other hand, because of the compression of the gas in the receiving tank. Joule-Thomson heating occurs along the line and the accessories, especially the valves, hoses and pipes, comprising the filling circuit. As regards the heating by compression of the gas, this is due to introduction of enthalpy into the tank via the supply gas: by being compressed, the gas inside the tank rises in temperature. The combined effect of these phenomena is the release of heat.
Simultaneously with this heating there is heat dissipation from the gas to the walls of its tank and then to the environment of the tank. This dissipation depends on the thermal properties of the gas, on the tank, on the ambient temperature and on the initial filling conditions. The heating effect will be more pronounced or less pronounced than that of the dissipation effect depending on how the flow rate used during filling varies.
There are mathematical models for calculating the variation in the conditions of the gas inside the tank during filling as a function of certain parameters (such as the initial conditions, the environment and characteristics of the tank) and also the operational variables of the filling (conditions of the supply gas throughout the length of the filling operation and the flow rate during filling).
The following three articles give for example detailed information on mathematical models of this type:                [1] K. Barral, E. Werlen, P. Pisot and P. Renault, “Thermal effects related to H2 fast filling in high pressure vessels depending on vessels types and filling procedures: modeling, trials and studies”, European Hydrogen Energy Conference EHEC, Grenoble (France), September 2003;        [2] S. Pregassame, K. Barral, L. Allidieres, T. Charbonneau and Y. Lacombe, “Operation feedback of hydrogen filling station”, Hydrogen and Fuel Cells 2004 Conference and Trade Show (Toronto, September 2004);        [3] K. Barral, S. Pregassame and P. Renault, “Thermal effects of fast filling hydrogen compression in refueling stations”, 15th World Hydrogen Energy Conference, Yokohama (Japan), June 2004.        
Such models can be used for mathematically formulating optimization problems.